The effects of ocular diseases on visual function have been studied extensively, but few efforts have centered on the study of neuronal changes in the visual system accompanying the normal aging process. In studying vision and aging, it is important to separate those effects related to ocular disease from those due to aging per se. Loss of visual acuity and sensitivity in old age has often been attributed to aging changes in the eye itself. However, several workers, for example, Owsley in 1983, showed that optical factors including illuminance differences and acuity problems had no role in temporal visual deficits which occur in normal aging and suggested that neural changes play an important role in the visual system. In order to determine the neural changes and the nature of loss in the visual field in aging, the investigator initiated studies aimed at determining whether significant changes occur in the optic tract axons with age, and if chronic hypertension aggravated the effects. There is little information on changes in ganglion cells and axonal population in progressive aging, nor, as well, on the effects of chronic hypertension on retinal neurons or optic axons. The investigator proposes to study the effects of aging and hypertension on the morphometrics of optic nerve axons, myelination, vacuolation, and on the number of ganglion cells in the retinas of normotensive and spontaneously hypertensive rats at 6, 24, 48, 72, and 96 weeks of age, using light and electron microscopy. The research activity initiated during the current grant period, i.e., "The study of ultrastructure of Purkinje cells as it is affected by progressive aging and hypertension in rats" will be completed.